UNIVERSITI MALAYSIA PERLIS
DECLARATION OF THESIS
Author's full name ABDULLAH OMAR ALI ALDHAIBANI
Date of birth 11TH MARCH 1981
Title NEW SPECTRAL AMPLITUDE CODING OCDMA SYSTEM
USING ADAPTIVE MULTICARRIER MODULATION FOR NEXT GENERATION NETWORK
Academic Session : 2015/2016
I hereby declare that the thesis becomes the property of Universiti Malaysia Perlis (UniMAP) and to be placed at the library of UniMAP. This thesis is classified as:
D
CONFIDENTIAL (Contains confidential information under the Official Secret Act 1972)*D
RESTRICTED (Contains restricted information as specified by the organization where research was done)*•
OP~N
ACCESS I agree that my thesis is to be made immediately available as hard copy or on-line open access (full text)I, the author, give permission to the UniMAP to reproduce this thesis in whole or in part for the purpose of research or academic exchange only (except during a period of .... years, if so
requested above).
Certified by:
05305227
(NEW IC NO.1 PASSPORT No.) Date:
11 ;7 /2-
0 I!:>PROF. DR. SYED ALWEE ALJUNID SYED JUNID NAME OF SUPERVISOR
~R6P.\m. SfE"fI.w?rk?:o' s~o JU NIO
DEKAN
PUSAT PENGURUSAN PENYEUOIKAN & INOVASI
NOTES:
*
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ACKNOWLEDGEMENT
Praise and thanks to Allah (SWT) who gave me the strength and courage to proceed with our entire life. My most special thanks to Prof. Dr. Syed Alwee Aljunid, for supporting me through the doctoral process and for his academic advice. His guidance, ideas, encouragement, affable nature, kindness and support were greatly helpful. Even with his busy schedule, he spent considerable amount of time helping me through the different phases of this project. I would also like to thank my co-supervisor Prof. Madya. Ir. Anuar Mat Safar for his kind support, and suggestions. I would like to express sincere thanks to my co-supervisor Dr. Amir Razif (Allah Yarhamah) for his invaluable guidance throughout this project. Special acknowledgement to Dr. Rashidi Che Beson, for his valuable suggestions and for the many interesting discussions I have had with him. A special acknowledgment must be given to AL-Sheikh Eng. Abdullah Ahmed Bogshan for his help and support during my study.
I wish to thank my parents, my brothers and sisters for their daily prayers, giving me the motivation and strength, and encouraging me to accomplish and achieve my goals.
Last but not least, sincere thanks and gratitude to my lovely wife Munerra and my daughters Rana who inspired me by their, courage, support and patience throughout the period of my study. Also I would like to extend my sincere appreciation to all who has helped me in one way or another, which whose names are not mentioned . I am very grateful having all of you beside me. Thank you very much.
Abdullah Omar Ali Aldhaibani.
Universiti Malaysia Perlis (UniMAP)
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TABLE OF CONTENTS
PAGE
DECLARATION OF THESIS i
ACKNOWLEDGEMENT ii
TABLE OF CONTENTS iii
LIST OF TABLES ix
LIST OF FIGURES x
LIST OF ABBREVIATIONS xiii
ABSTRAK (MALAY) xvi
ABSTRACT (ENGLISH) xvii
CHAPTER 1 INTRODUCTION
1.1 Introduction 1
1.2 Problem Statement 2
1.3 Research Objectives 4
1.4 Scope of Works 5
1.5 Contributions of This Research 6
1.6 Thesis Outline 7
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 8
2.2 Multiple Access Techniques 10
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2.2.1 Wavelength Division Multiplexing Access 11
2.2.2 Time Division Multiple Access 13
2.2.3 Optical Code Division Multiple Access 14 2.2.3.1 The Spectrum-Amplitude Coding (SAC) OCDMA
Network
19
2.3 Optical Hybrid Multiple Access 21
2.4 Optical Modulation 23
2.4.1 Pulsed Modulation Techniques 24
2.4.2 Optical OFDM Modulation 26
2.4.2.1 DCO-OFDM 32
2.4.2.2 ACO-OFDM 33
2.5 Summary 34
CHAPTER 3 DEVELOPMENT OF NEW SAC-OCDMA SYSTEM
3.1 Introduction 35
3.2 Methodology 35
3.3 SAC-OCDMA Code Design 37
3.4 Modified Double Weight (MDW) Code 39
3.4.1 MDW Code Design Steps 39
3.4.2 Properties of MDW Code 43
3.4.3 Encoding/Decoding Process of MDW Code 44
3.5 Flexible Cross Correlation Code (FCC) 45
3.5.1 Code Design Algorithm 46
3.5.2 FCC Code Properties 48
3.6 RF-Multicarrier Modulation: OFDM Modulation 51
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3.6.1 Cyclic Prefix for OFDM 54
3.6.2 Direct Detection Optical OFDM 56
3.7 Principle of the Proposed OCDMA Using OFDM Scheme 56
3.8 Simulation Analysis 58
3.8.1 Design Parameter 59
3.8.1.1 Distance 59
3.8.1.2 Bit Rate 59
3.8.1.3 Bit Error Rate 60
3.8.1.4 Transmission Power 61
3.8.1.5 Chip Spacing 61
3.8.1.6 Received Power (Output Power) 61
3.8.1.7 Noise Power 62
3.9 Summary 62
CHAPTER 4 THEORETICAL ANALYSIS OF A SAC-OCDMA SYSTEM USING OFDM MODULATION AND A SCM/SAC-OCDMA SYSTEM
4.1 Introduction 63
4.2 Noises in SAC-OCDMA Networks 63
4.2.1 Thermal Noise 64
4.2.2 Shot Noise 65
4.2.3 Phase Induced Intensity Noise (PIIN) 67
4.2.4 Third Order Intermodulation (IM3) 68
4.3 Multiple Access Interference (MAI) 70
4.4 Detection Schemes for SAC-OCDMA Systems 72
4.4.1 AND Subtraction Technique 72
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4.5 BER Generation of an SAC-OCDMA System with OFDM Modulation Based on MDW Code
74 4.6 Performance of Subcarrier Multiplexed SCM/SAC-OCDMA System Using
MDW Code
83
4.6.1 RF-Subcarrier Multiplexed SAC-OCDMA System Architecture 84 4.6.2 The BER Analysis of an SCM/SAC-OCDMA System Based on
MDW Code
86
4.6 Summary 90
CHAPTER 5 RESULTS AND DISCUSSION
5.1 Introduction 92
5.2 OCDMA/OFDM Mathematical Analysis Results 92
5.2.1 Effect of the Number of Users on System Performance Considering All System Noises
94
5.2.2 Variation of SNR as a Function of the Number of Users 95 5.2.3 Effect of Number of Users on Average Signal Power 96 5.2.4 Variation of BER as a Function of the Number of Users and
Effective Power with MDW Code For a SAC-OCDMA_OFDM System
97
5.2.5 Variation of BER as a Function of the Number of Users and Effective Power with FCC Code For the OCDMA_OFDM System
98
5.2.6 Variation of BER as a Function of the Number of Users and Effective Power for SCM/OCDMA-MDW and OFDM_OCDMA- MDW
99
5.2.7 Relationship Between Received Power and PIIN Noise 100
5.2.8 Effect of Received Power on Shot Noise 101
5.2.9 The Effect of IMD3 Noise on the Number of Subcarrier 103 5.2.10 Effect of Received Power Psr on System Performance 104 5.2.11 BER Variation as a Function of Various Data Rates for OCDMA_
OFDM and OCDMA with MDW Code
105
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5.2.12 BER Variation as a Function of Number of Data Rate for OCDMA_ OFDM and OCDMA with FCC Code
106
5.2.13 Variation of BER with Number of Users by Considering the Effect of Weights for the OFDM/SAC-OCDMA System using MDW Code
107
5.2.14 Variation of BER as a Function of the Number of Users and Effective Power for SCM/SAC-OCDMA_FCC
108
5.2.15 Variation of Power Received with BER in an SCM/SAC-OCDMA System Based on FCC and MDW Codes
109
5.2.16 BER Variation as a Function of Number of User for SAC- OCDMA_ OFDM and SAC-OCDMA Based on MDW Code
110
5.2.17 BER Variation as a Function of Data Rate for SAC-OCDMA_
OFDM and SAC-OCDMA with MDW Code
111 5.2.18 Variation of BER with Simultaneous Users for All Systems 112
5.3 Simulation Results 113
5.3.1 The Electrical Spectra and Constellation Diagram 115 5.3.2 The Effect of Cyclic Prefix on The Performance 116 5.3.3 The Effect of Distance on Signal to Noise Ratio (SNR) 119
5.3.4 The Effect of Distance on Total Power 120
5.3.5 Effect of Chip Spacing in The Network 120
5.3.6 SNR Variation as a Function of Data Rate 121
5.3.7 Comparison Between Theoretical and Simulation Results for SAC- OCDMA/OFDM Modulation
122 5.3.8 SAC-OCDMA/OFDM Modulation with Zero Cross Correlation
Code Family
124
5.4 SAC-OCDMA/OFDM Modulation Application 126
5.5 Summary 128
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CHAPTER 6 CONCLUSION AND FUTURE WORKS
6.1 Conclusion 129
6.2 Future Works 132
REFERENCES 133
LIST OF PUBLICATIONS 147
LIST OF AWARDS 150
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LIST OF TABLES
NO. PAGE
3.1 The FCC code with K = 4, W = 3, λc ≤1 and N=9 48
3.2 Typical OFDM system versus typical optical system 52 4.1 Important symbols and parameters used in equations 76
5.1 Parameters for mathematical analysis 93
5.2 Performance of SAC-OCDMA/OFDM system as data rate varied 106 5.3 Cardinality improvement of SAC-OCDMA/OFDMM over other
systems
113
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LIST OF FIGURES
NO. PAGE
2.1 Comparison of three multiple access techniques TDM, WDM and OCDMA
11
2.2 WDMA block diagram 12
2.3 TDMA block diagram 13
2.4 Schematic diagram of an OCDMA system 15
2.5 Principle of SAC- OCDMA scheme 20
2.6 Hybrid WDM/OCDMA 22
2.7 Block diagram of a SCM/OCDMA system 23
2.8 Demonstrating SC pulsed modulation schemes, OOK and PPM 26 2.9 Comparison of Single carrier, General frequency division
multiplexing and, Orthogonal frequency division multiplexing
28
2.10 Demonstrating SSM and MSM 29
2.11 An optical OFDM modulation at transmitter 31
3.1 Scope of new development SAC-OCDMA system using OFDM modulation
37
3.2 General form of the MDW code matrix 40
3.3 Flowchart for the MDW code design algorithm 44
3.4 MDW code encoder decoder implementation 45
3.5 Identification used in FCC code 48
3.6 Flowchart for the FCC code design algorithm 51
3.7 OFDM symbol with cyclic prefix 56
3.8 Schematic of the transmitter and receiver using amplitude spectral coding with OFDM
58
4.1 The spectrum of a nonlinear system with equally spaced tones and constant amplitude
70
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73
4.3 OFDM/SAC-OCDMA scheme 75
4.4 Bandwidth of broadband source at the receiver 78
4.5 Output spectrum of a nonlinear system excited by (n) equally spaced tones with constant amplitude
82
4.6 SCM/SAC-OCDMA based on MDW code 85
5.1 BER versus number of active users considering all noise 94 5.2 Performance of SNR versus simultaneous number of users for
OCDMA system using OFDM modulation
95
5.3 Average signal power performance versus number of active users for the OFDM/SAC-OCDMA system
96
5.4 BER versus number of simultaneous users for the different values of Psr based on the MDW code
97
5.5 BER versus number of simultaneous users for different values of Psr based on FCC code
98
5.6 BER against the number of active users when Psr is different for OFDM/SAC-OCDMA_MDW and SCM/SAC-OCDMA_MDW systems
99
5.7 PIIN noise versus received power (Psr ) 101
5.8 Shot noise versus Psr for various SAC-OCDMA codes using OFDM modulation
102
5.9 IMD3 versus the number of subcarrier for SAC-OCDMA/OFDM system
103
5.10 BER versus received power 104
5.11 BER versus number of users with different data rate 105 5.12 BER versus number of users for SAC-OCDMA_OFDM system
with FCC (W=4) code
106
5.13 BER versus number of user with different code weights 107
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5.14 BER versus total number of users for the hybrid SCM/SAC- OCDMA system
108
5.15 BER versus power receives for SCM/OCDMA system based on MDW and FCC codes
109
5.16 Number of users versus BER for OFDM/SAC-OCDMA and SAC- OCDMA systems
110 5.17 BER versus number of users with various data rate 111
5.18 BER versus number of users for different systems 112
5.19 Block diagram of the SAC-OCDMA_OFDM system 114
5.20 (a) The electrical spectra of the optical OFDM signals at the transmitter
115
5.20 (b) The electrical spectra of the optical OFDM signals at the receiver
115
5.21 QAM constellation diagram for the received signal 115
5.22 SNR versus cyclic prefix points 117
5.23 Power penalty versus cyclic prefix points 118
5.24 Power receive (Psr) versus cyclic prefix points 118
5.25 SNR versus fiber lengths 119
5.26 Total power versus distance for proposed system 120
5.27 The effect of spacing on SNR and distance 121
5.28 SNR versus the data rate with different distances 122
5.29 Signal power versus distance 122
5.30 SNR versus distance for SAC-OCDMA/OFDM system 123
5.31 Implementing of SAC-OCDMA with OFDM modulation based on MD code using direct detection technique
124
5.32 BER versus different values of data rate 125
5.33 BER versus distance 126
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LIST OF ABBREVIATIONS
BER Bit Error Rate
BPSK Binary Phase Shift Keying BS Brillouin Scattering
CDMA Code Division Multiple Access CD Chromatic Dispersion
CSK Code-Shift-Keying CP Cyclic Prefix
CW Continuous Wave
DPSK Differential Phase-Shift Keying
DQPSK Differential Quaternary Phase Shift Keying DMUX De-Multiplexer
EDFA Erbium Doped Fiber Amplifier EDW Enhanced Double Weight FBG Fiber Bragg Grating FCC Flexible Cross Correlation FFT Fast Fourier Transform FSO Free Space Optics FTTH Fiber To The Home FWM Four Wave Mixing Gb/s Gigabit per second ICI Inter-Carrier Interference IFFT Inverse Fast Fourier Transform IMD3 Third Intermodulation Distortion
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xiv ISI Inter-symbol Interference LAN Local Area Network LED Light Emitting Diode LiNbO3 Lithium-Niobate
MAI Multiple Access Interference Mb/s Mega bit per second
MCM Multi-Carrier Modulation MD Multi Diagonal
MDW Modified Double Weight MFH Modified Frequency Hoping
MOD Modulator
MQC Modified Quadratic Congruence MSM Multiple-Subcarrier Modulation MUX Multiplexer
MZ Mach-Zehnder
NRZ Non Return to Zero OOC Optical Orthogonal Code OEM Optical Electrical Modulator
OCDMA Optical Code Division Multiple Access OOK On-Off Keying
OFDM Orthogonal Frequency Division Multiplexing OSCDM Optical Spectrum Code Division Multiplexing PAPR Peak-to-Average-Power Ratio
PIIN Phase Induced Intensity Noise PIN Positive Intrinsic Negative
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xv PMD Polarization Mode Dispersion PON Passive Optical Networks
PRBS Pseudo Random Binary Sequence PSD Power Spectral Density
QoS Quality of Service
QAM Quadrature Amplitude Modulation RD Random Diagonal
RF Radio Frequency RoF Radio Over Fiber RZ Return to Zero
SAC Spectral Amplitude Coding SCM Subcarrier Multiplexing SC Single Carrier
SLD Super Luminescent Diode SMF Single Mode Fiber
SNR Signal to Noise-Ratio
SSM Single-Subcarrier Modulation SPC Spectral Phase Coding
TDM Time Division Multiplexing TDMA Time Division Multiple Access PSK Phase-Shift Keying
PPM Pulse-Position Modulation WAN Wide Area Network
WDM Wavelength Division Multiplexing WDMA Wavelength Division Multiple Access
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Sistem Baru Spektrum Amplitud Pengekodan OCDMA Menggunakan Adaptive Multicarrier Modulation Untuk Rangkaian Generasi Masa Depan
ABSTRAK
Teknik pengekodan kod optik spektrum Amplitud multi capaian (SAC-OCDMA) membolehkan ramai pelanggan untuk berkongsi rangkaian yang sama serentak dan tak serentak dengan memperuntukkan satu kod yang khusus untuk setiap pelanggan.
Prestasi sistem SAC-OCDMA ditentukan oleh pelbagai parameter seperti kadar data, jumlah pengguna serentak, kuasa pemancar dan penerima, dan jenis kod. Oleh itu, sistem SAC-OCDMA mempunyai had dalam bilangan pengguna dan kadar bit kerana gangguan multi capaian (MAI), yang dianggap sebagai faktor kemerosotan dominan dalam sistem SAC-OCDMA. Dalam kajian ini, satu pendekatan baru kepada sistem SAC-OCDMA dengan penyesuaian modulasi multicarrier (OFDM) telah dibangunkan untuk menampung jumlah pengguna yang besar, meningkatkan keupayaan sistem, dan mengurangkan degradasi sistem. Sistem yang dicadangkan itu telah dibina menggunakan kod dari keluarga MDW, yang mempunyai pelbagai kelebihan berbanding kod lain termasuk pembinaan kod yang mudah, reka bentuk pengekod/penyahkod yang mudah, kewujudan abgi setiap nombor asli n, korelasi-balas ynag sesuai(λ = 1) dan SNR yang lebih tinggi . Rangka kerja baru matematik untuk mengira SNR dan BER sistem SAC-OCDMA menggunakan penyesuaian modulasi berbilang pembawa (OFDM) telah dibangunkan dan dianalisis berdasarkan teknik AND pengesanan. Ia menyediakan penggunaan spektrum yang lebih baik, menjana jumlah yang lebih tinggi daripada sub-pembawa, dan meningkatkan kadar penghantaran menggunakan komponen optik kos rendah oleh modulasi M-ary pada sub-pembawanya.
Selain itu, model matematik dan hasil, berdasarkan kod dan teknik pengesanan yang sama untuk menguji semua reka bentuk yang mungkin, telah dihasilkan untuk sistem SCM/SAC-OCDMA . Berdasarkan pengiraan matematik, sistem SAC-OCDMA dengan penyesuaian modulasi berbilang pembawa (OFDM) telah menunjukkan prestasi yang membanggakan berbanding SCM/SAC-OCDMA dan sistem SAC-OCDMA konvensional. Keputusan teori dan simulasi telah dinilai berdasarkan BER dan bilangan pengguna dan juga jumlah kuasa dikekalkan. Perisian Optisys (Versi 12) telah digunakan untuk mensimulasikan sistem yang direka. Sistem yang dicadangkan memberi prestasi yang lebih baik dengan mengekalkan lebih kurang 40% kuasa serta meningkatkan bilangan pengguna dua kali ganda berbanding dengan sistem SCM/SAC- OCDMA. Pembesaran prestasi, dari segi bilangan pengguna, untuk SAC-OCDMA dengan modulasi multicarrier penyesuaian (OFDM) berbanding dengan sistem SCM/SAC-OCDMA adalah dua kali dan tiga kali berbanding sistem SAC-OCDMA konvensional berdasarkan kod MDW. Pembangunan sistem baru ini telah menyumbang kepada peningkatan sistem SAC-OCDMA dengan mengurangkan gangguan, meningkatkan kadar data saluran, mengekalkan kuasa, dan meningkatkan bilangan pengguna. Oleh itu, sistem ini boleh menjadi penyelesaian mutlak untuk rangkaian akses kapasiti yang tinggi simetri kerana kecekapan spektrum yang tinggi, keberkesanan kos, fleksibiliti yang baik, dan keselamatan yang dipertingkatkan. Ciri-ciri ini menjadikan ia calon menarik bagi rangkaian jalur lebar akses generasi akan datang.
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New Spectral Amplitude Coding OCDMA System Using Adaptive Multicarrier Modulation for Next-Generation Networks
ABSTRACT
The spectral amplitude coding optical code division multiple access (SAC-OCDMA) technique enables many subscribers to share a network simultaneously and asynchronously by allocating a specific code to each subscriber. The performance of the SAC-OCDMA systems is governed by numerous parameters such as the data rate, number of simultaneous users, the powers of the transmitter and receiver, and the type of codes.Therefore, a SAC-OCDMA system has limitations in the number of users and bit rate because of multiple access interference (MAI) which is considered to be the dominant degradation factor in SAC-OCDMA systems. In this work, a new approach to the SAC-OCDMA system with Rf-subcarrier such as adaptive multicarrier modulation (OFDM) has been developed, to accommodate a large number of users, enhance the system capacity, and decrease the system degradation. The proposed system has been built using the modified double weight (MDW) code family, which has various advantages over other codes including easy code construction, simple encoder/decoder design, existence for every natural number n, ideal cross-correlation (λ = 1) and a higher SNR.A new mathematical framework to calculate the SNR and the BER of the SAC- OCDMA system usingadaptive multi-carrier modulation (OFDM) has been developed and analysed based on the AND detection technique. Itprovides better spectrum use, generates a higher number of sub-carriers, and increases transmission rates using low- cost optical components by M-ary modulation on its sub-carriers. In addition, mathematical models and results, based on the same code and detection technique in order to test all possible design, have been generated for the Rf-SCM/SAC-OCDMA system. Based on the mathematical calculations, the SAC-OCDMA system with adaptive multi-carrier modulation (OFDM) has shown superior performance compared to Rf-SCM/SAC-OCDMA and conventional SAC-OCDMA systems. The theoretical and simulation results have been evaluated based on the BER and number of users as well as on the amount of power maintained.Optisys (version 12), software was used to simulate the designed system. The proposed system gave better performance and maintained approximately 40% of power as well as increased the number of users twofold compared to Rf-SCM/SAC-OCDMA system. Augmentation in performance, in terms of the number of users, for SAC-OCDMA with adaptive multicarrier modulation (OFDM) compared to a conventional SAC-OCDMA systems based on MDW code is more than three times. The development of this new system has contributed to SAC- OCDMA system improvement by mitigating the interference, enhancing the channel data rate, maintaining the power, and increasing the number of users. Thus, this system could be a promising solution to symmetric high capacity access networks because of its high spectral efficiency, cost effectiveness, good flexibility, and enhanced security.
These features make it an attractive candidate for next-generation broadband-access networks.
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1 CHAPTER 1
INTRODUCTION
1.1 Introduction
Currently, telecommunication systems and networks are extended to provide a variety of multimedia applications such as video streaming, voice-over-IP and gaming.
The resulting demand for bandwidth requires a network infrastructure that has a large capacity and is reconfigurable.Optical fibres can fulfil the bandwidth demand of future information networks through optimizing the available bandwidth by multiplexing low- rate data streams onto optical fiber. For this purpose, multiple access schemes, such as Time Division Multiple Access (TDMA), Wave Division Multiple Access (WDMA), and Optical Code Division Multiple Access (OCDMA), are required for multiplexing and demultiplexing data flow.
The multiplexing technique is the process whereby several optical signals are combined before being transmitted through a fiber optic (Kolimbiris, 2004). In other words, multiplexing techniques are multiple access communication systems whereby a number of users share a common transmission media to transmit their messages to a number of destinations.
In recent years, OCDMA has been an emerging research area that has attracted a lot of research interest because of the demand for OCDMA application in optical networks. It offers a large bandwidth, security, and flexibility in high speed access networks. Moreover, OCDMA has some unique advantages such as, asynchronous transmission with low latency access, dynamic bandwidth assignment, soft capacity on demand, random and simultaneous access protocols, simplified network control, effective bandwidth utilization, increased flexibility in quality of service control
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(Prucnal, Santoro, & Fan, 1986) and enhanced network security (Chung, Salehi, & Wei, 1989).Different multiplexing techniques are discussed in more detail in chapter 2.
1.2 Problem Statement
Huge demand for multimedia data, higher data speeds (such as for high- definition video) and an increasing number of users are putting pressure on optical transmission systems and network vendors to offer higher data rates (Shaddad, R. Q., et al., 2012). Reducing this pressure could be achieved by using optical techniques that can provide sufficient bandwidth for these applications (Elmagzoub, M. A., et al., 2014).
Therefore, there is a search for a sufficient optical approach that enables the necessary bandwidth to accommodate a large number of users, high data rates, and intensive applications at a cost-effective rate.For this purpose, multiple access schemes such as OCDMA, optical TDMA and optical WDMA, are required for multiplexing and demultiplexing data flow. The operation of an OTDMA system is limited by the time- serial nature of the technology. Each receiver should operate at the total bit rate of the system. The OTDMA system requires synchronization and centralized control. The users are allocated a specific time slot.However in OCDMA system, users can operate asynchronously and access the network independently.
In WDMA systems, the available optical bandwidth is divided into fixed wavelength channels that are used concurrently by different users. Thus, an issue with WDMA is that wavelength-cardinality is limited, in that the WDMA systems can only handle traffic on an optical channel of the wavelength path. This may waste wavelength resources.
In recent years, OCDMA has received more attention because of its potential for enhanced information security, simplified and decentralized network control,
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allowing many users to share the same transmission medium synchronously and simultaneously as well as for increased flexibility in the granularity of bandwidth that can be provisioned (Sahbudin, et al., 2009; Salehi J A, 2007; Stok & Sargent, 2002a;
Weng & Wu, 2001).
There are several challenges, such as multiple access interference (MAI), which results from other users transmitting at the same time and on the same common channel (Aljunid, Ismail, et al., 2004a). Furthermore, there are other noises arising from the physical effect of the system design itself, such as phase induced intensity Noise (PIIN), thermal noise, and shot noise (Shin-Pin & Jingshown, 2010). The PIIN is related to the MAI because the overlapping (cross-correlation function) of the spectra from different users (Aljunid, Ismail, et al., 2004a). Moreover, increases in cardinality (number of simultaneous users) results in long code length and weight. As a consequence, the (PIIN) increases, causing deterioration in BER and system performance. In addition, the spectral amplitude coding optical division multiplexing (SAC-OCDMA) is needed to improve the spectral efficiency. There are several optical modulation techniques used in an OCDMA system such as on-off keying (OOK) but it is not efficient at very small duty cycles. Consequently, it is more appropriate to code the information into the position of the pulse such as in pulse-position modulation (PPM). PPM imposes more system complexity than OOK because both slot- and symbol-level synchronizations, critical to system performance, are required at the receiver. Multipath propagation induces inter-symbol interference (ISI) and PPM is particularly sensitive to the dispersive effects of the optical channel due to the required bandwidth (Audeh, M. D.
1996).
To avoid ISI channels, single carrier (SC) pulsed modulation is used, but it results in severe performance penalties. Several equalization techniques, for example,
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using linear and decision feedback equalizers (DFEs), are considered to mitigate the effects of ISI at high data rates and it, as well, is required for detecting the aggregate high-speed bit stream.The drawbacks of SC pulsed modulation are overcome by using an alternative modulation technique—multiple-subcarrier modulation (MSM).
Hybrid subcarrier multiplexing (SCM) has increased the number of users and enhanced the channel data rate for OCDMA systems, but an SCM/OCDMA system has the disadvantage of being limited, by the available bandwidth of the electrical and optical components, in the maximum subcarrier frequencies and data rates. Adaptive multi-carrier OFDM modulation avoids these problems by generating a huge number of sub-carriers, as it is more accurate to assign a limited number of sub-carriers for each user. Moreover, OFDM is an effective solution to inter-symbol interference caused by a dispersive channel.
1.3 Research Objectives
The aim of this research is to develop a new spectral amplitude coding OCDMA system using adaptive multicarrier modulation for next-generation networks which can be superior to the performance of SAC-OCDMA systems. To achieve the aim of this research, the following objectives can be summarized as:
To develop a new approach to SAC-OCDMA systems with OFDM modulation to enhance the system capacity and decrease the system degradation.
To develop a mathematical model of the new SAC-OCDMA system using OFDM modulation based on an AND detection technique.
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To analyse the theoretical and simulated performance of the SAC-OCDMA system using OFDM modulation.
To analyse the performance of an SCM/SAC-OCDMA system based on the MDW code family with the AND detection technique.
1.4 Scope of Work
Currently, internet network architecture can be divided into several different layers according to, each layer’s specific function, components, and protocols. The scope in this research is the physical layer—which defines the physical specifications for devices—and the relationship between a device and a transmission medium. In the case of fiber-optical networks, the transmission medium is optical fiber. The physical layer is involved in converting electronic data into modulated light signals and transmitting it through the optical fiber. To transmit the data for multiple users, multiplexing, multiple access techniques are used here. Standard parameters that are considered here are the bit-error rate (BER), signal to noise ratio (SNR), and receiver power and loss. In this work the focus is on the security issues of the physical layer. A spectrum amplitude code division multiplexing technique (SAC-OCDMA) is used and applied to secure and protect the data transmitted through networks and to conduct decryption of the received data before passing it to the application layer. Also, here there is a focus onOFDM modulation techniques to increase the overall performance of the system based on an MDW code family. In addition to using subcarrier multiplexing with the SAC-OCDMA system, the subcarrier techniques are compared with conventional systems as well as the comparison between hybrid SCM and OFDM modulation techniques with conventional SAC-OCDMA system.
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6
In this work, Firstly, a new optical orthogonal frequency division multiplexing (OFDM) modulation with spectrum amplitude coding optical code division multiple access (SAC-OCDMA) system is developed. Secondly, developing the mathematical model for a new SAC-OCDMA system using adaptive OFDM modulation and comparing it with both hybrid SCM/SAC-OCDMA and conventional SAC-OCDMA systems.
Considering back to back systems, which mean no effect of the distance impairment.
Lastly, the performance simulation of the SAC-OCDMA system using adaptive OFDM is provided. Optisys software was used for the simulation.
1.5 Contributions of This Research
A new approach for spectral-amplitude coding systems is developed to enhance the performance of OCDMA systems using OFMD modulation. The proposed contributions are summarized in the following:
I. A new SAC-OCDMA system with adaptive multicarrier modulation (OFDM) was developed.
II. A new mathematical model of the SNR and BER for the new system with an AND detection technique based on MDW code family has been developed and thoroughly analyzed.
III. Development of a SCM/SAC-OCDMA system and its mathematical model of SNR and BER based on an MDW code family with same detection technique were performed.
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7 1.6 Thesis Outline
This thesis comprises of six (6) chapters, and it is organized as follows:
i. Chapter 1 is an overview and problem statement that clarifies the driving force and motivating aspect, together with the objectives, scope of work,contributions and thesis layout.
ii. Chapter 2 a literature review of OCDMA communication systems and optical hybrid multiple access and optical modulation techniques. In addition, some optical modulations such as optical orthogonal frequency division multiplexing (OFDM) and pulsed modulation techniques are described.
iii. In chapter 3 the research methodology is described and a detailed explanation of the design of codes used for the spectral amplitude coding OCDMA system, known as the modified double weight (MDW) code and flexible cross- correlation (FCC) code is given. The OFDM modulation with direct detection technique also described and simulation analysis.
iv. In chapter 4 the proposed signal-to-noise ratio (SNR) mathematics for a SAC-OCDMA system using OFDM modulation and a SCM/SAC-OCDMA system based on MDW code is presented.
v. In chapter 5 the results and the performance analysis of the new system using MDW and FCC codes are discussed and the feasibility of the system is demonstrated.
vii. Chapter 6 is the conclusion of the thesis; the most important ideas are summarized, and ideas for future work are given.
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